The present invention is directed to an improvement on the invention disclosed in U.S. Pat. No. 3,703,465, assigned to the assignee of the present invention.
In known rotating backwash arm filter assemblies, including that of the above-mentioned patent, wherein the array of filter units and the rotatable backwash arm extend axially from each other, the backwash fluid outlet ends of the filter unit are normally coplanar and communicate through openings in a partition with the portion of the housing in which the backwash arm is located. In such known arrangements, sequential backwashing of the filter units is accomplished solely by rotation of the backwash arm from filter unit to filter unit and the adjacent end portion of the backwash arm is in continuous contact with the opposed face of such partition. In an attempt to maintain a degree of backwash efficiency, the orbiting end of the backwash arm is normally provided with an annular seal engageable with the opposed surface of such partition to limit leakage of fluid flowing between the arm and an opposed filter unit and leakage between arm and partition, and to obtain even minimal sealing, the arm end seal must be axially urged against the partition with substantial force. On the other hand, as the arm angularly indexes from one filter unit to the other, the seal scrubs along the face of the partition. Thus, a rotation drive motor of considerable power and hence size is required to rotate the arm in view of the relatively high starting and running friction between the seal and partition. Further, frictional wear on the opposed faces of the partition and seal, particularly the latter, is relatively rapid, normally requiring relatively frequent seal replacement. Such power and wear considerations appear despite compromising of seal effectiveness due to limiting the force of compressive contact between the seal and partition.
Further, and as a practical matter, the partition in a given production filter assembly may be less than perfectly flat and/or may be somewhat cocked with respect to the arm rotational axis. This tends to promote imperfect sealing and leakage in backwashing of one or more of the array of filter units. Attempts to overcome this problem have included use of very soft flexible arm end seals which tend to wear even more rapidly and may, in use, distort sufficiently to partially block backwash fluid flow between the arm and opposed filter unit. Such attempts have also included use of spring-loaded multi-part seals, which are relatively complex mechanically and relatively expensive and typically involve additional sealing faces internally of the seal itself.
In addition, prior assemblies of this type have typically employed either a manual rotation of the arm or a rotatable motor (e.g. electric) wherein rotational indexing of the arm may be relatively imprecise, due to difficulty in precisely stopping motor rotation with the arm precisely coaxial with the next filter unit to be backwashed. In other prior assemblies the arm rotated continuously, thereby limiting adjustability of backwash time.
Accordingly, the objects of this invention include provision of:
1. A filter assembly having an improved rotating arm backwash system for improving backwash efficiency and reducing backwash fluid leakage.
2. A filter assembly, as aforesaid, which provides for positive sealing of the opposed backwash arm and filter unit end, and permits substantially increased compressive axial sealing forces therebetween for substantially eliminating leakage, while permitting use of an inexpensive one-piece seal of simplified construction.
3. A filter assembly, as aforesaid, which at least substantially eliminates (and in a preferred embodiment eliminates) lateral sliding contact between the arm seal and opposed partition or filter unit end faces during rotational indexing of the arm from one filter unit to the next, which eliminates scuff wear on such opposed sealing faces, and which does so without inducing backwash fluid leakage.
4. A filter apparatus, as aforesaid, which permits substantial increases in acceptable tolerances for partition flatness and coplanarity of filter unit backwash fluid outlet ends and for perpendicularity of the backwash arm rotation axis to such partition or the plane of such filter unit end, without reduction of backwash efficiency or promotion of backwash fluid leakage.
5. A filter assembly, as aforesaid, wherein the backwash arm and its end seal are maintained out of contact with and somewhat spaced from the partition and opposed filter unit ends during at least the major portion (all in a preferred embodiment) of rotation from filter unit to filter unit.
6. A filter unit, as aforesaid, in which positive and precise angular location of the backwash arm, in coaxial relation to each of the filter units is achievable, wherein circumferential offsetting therebetween and consequent cross-sectional restriction of backwash flow is eliminated, and wherein a rotational indexing unit of positive type is employed.
7. A filter unit, as aforesaid, wherein a substantial axial sealing force is achievable with a relatively small, low force motor means wherein a mechanical advantage is provided between such motor means and arm.
8. A filter assembly, as aforesaid, wherein the rotating arm unit is readily adaptable to a variety of previously manufactured filter assemblies, which may be in present use, as well as to inclusion in new filter assemblies during manufacture, and wherein the rotating arm unit is readily adaptable to filter assemblies having filtering units of different size, circumferential spacing, quantity and so forth with minimal and readily carried out substitution of parts.
9. A filter assembly, as aforesaid, wherein the backwash system is rugged and reliable in construction, relatively simple in construction and low in cost, and readily repairable if necessary.
10. A filter assembly, as aforesaid, which substantially eliminates breakage of rotating arm unit parts, particularly should sticks, pieces of metal, or other relatively rigid debris, become lodged in the path of parts of the rotating arm unit and wherein the rotational indexing and axial shift drive for the rotating arm employ force generating means of resilient type.
11. A filter assembly, as aforesaid, which may utilize for backwashing either filtrate or separate backwashing fluid.
Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.